The effects of physical activity on impulsive choice: Influence of sensitivity to reinforcement amount and delay

Abstract

Impulsive choice is a diagnostic feature and/or complicating factor for several psychological disorders and may be examined in the laboratory using delay-discounting procedures. Recent investigators have proposed using quantitative measures of analysis to examine the behavioral processes contributing to impulsive choice. The purpose of this study was to examine the effects of physical activity (i.e., wheel running) on impulsive choice in a single-response, discrete-trial procedure using two quantitative methods of analysis. To this end, rats were assigned to physical activity or sedentary groups and trained to respond in a delay-discounting procedure. In this procedure, one lever always produced one food pellet immediately, whereas a second lever produced three food pellets after a 0, 10, 20, 40, or 80-s delay. Estimates of sensitivity to reinforcement amount and sensitivity to reinforcement delay were determined using (1) a simple linear analysis and (2) an analysis of logarithmically transformed response ratios. Both analyses revealed that physical activity decreased sensitivity to reinforcement amount and sensitivity to reinforcement delay. These findings indicate that (1) physical activity has significant but functionally opposing effects on the behavioral processes that contribute to impulsive choice and (2) both quantitative methods of analysis are appropriate for use in single-response, discrete-trial procedures.

Keywords: Delay discounting; Exercise; Female; Impulsive choice; Physical activity.

Figure 1

Wheel running in seven physical activity rats. Data depict wheel revolutions/day (×1000) plotted as a function of time (expressed in “weeks” of 5- to 10-day intervals). Reference line after week 6 (vertical broken line extending from abscissa) indicates the beginning of behavioral training.

Figure 2

Delay discounting in six sedentary rats. The percentage of responses allocated to the larger, later reinforcer lever (%LLR) are plotted as a function of delay interval (s). All plots depict data averaged across the last 12 consecutive days of testing.

Figure 3

Delay discounting in seven physical activity rats. The percentage of responses allocated to the larger, later reinforcer lever (%LLR) are plotted as a function of delay interval (s). All plots depict data averaged across the last 12 consecutive days of testing.

Figure 4

Group delay discounting performance. The percentage of responses allocated to the larger, later reinforcer lever (%LLR) are plotted as a function of delay interval (s). All plots depict data averaged across the last 12 consecutive days of testing. Physical activity rats are represented by closed circles and the dotted line and sedentary rats by open circles and the solid line. Asterisks (*) indicate significant differences between groups as determined by independent-samples t-tests.

Figure 5

Sensitivity to reinforcement amount and delay in six sedentary rats. Log response ratios are plotted as a function of log delay ratios using a linear equation. All plots depict data averaged across the last 12 consecutive days of testing.

Figure 6

Sensitivity to reinforcement amount and delay in seven physical activity rats. Log response ratios are plotted as a function of log delay ratios using a linear equation. All plots depict data averaged across the last 12 consecutive days of testing.

Figure 7

Sensitivity to reinforcement amount (y-intercept: top left panel; S_A: bottom left panel) and sensitivity to reinforcement delay (slope: top right panel; S_D: bottom right panel). Data are shown for six sedentary rats (filled symbols) and seven physical activity rats (open symbols). Solid horizontal lines indicate group averages. Slope and y-intercept were derived from simple regression equation with %LLR as the criterion and delay interval (s) as the predictor. S_A and S_D values were derived from logarithmically transformed values as depicted in Figures 5 and 6. All values reflect the average from the last 12 consecutive days of testing.

Figure 8

Correlation between measures of sensitivity to reinforcement amount and between measures of sensitivity to reinforcement delay. Correlations represent comparisons of simple linear regression (x-axis) and logarithmically transformed equation (y-axis) estimates. The left panel plots the correlation between simple regression y-intercept and logarithmically transformed equation S_A values (sensitivity to reinforcement amount). The right panel indicates correlation between simple regression slope and logarithmically transformed equation S_D values (sensitivity to reinforcement delay).

Figure 9

Sensitivity to reinforcement amount (y-intercept: top left panel; S_A: bottom left panel) and sensitivity to reinforcement delay (slope: top right panel; S_D: bottom right panel) in sedentary (black bars) and physical activity (gray bars) rats. Data reflect averages from the final two, six, and twelve consecutive days of testing. Asterisks (*) indicate significant differences between groups as determined by independent-samples t-tests.